Here's an example: Let's say people are talking about which cameras to buy, and you want to talk about digital SLRs - for that you should create a sub-page for digital SLR cameras. But then someone else wants to talk about video cameras - that is not a sub-page off the digital SLR cameras page, but a sub-page off the original camera page.

So when you add content, think if you are writing it in the right place, and enjoy adding to the fund of knowledge which the wiki pages will be by making it really useful, like wikipedia.